This invention relates to an electronic control unit having a single non-volatile memory for multiple central processing units.
An electronic control unit (ECUs) for engines or vehicles use multiple central processing units (CPUs) and non-volatile memories such as electrically erasable programmable read-only memories (EEPROMs). The EEPROM is used to store therein, even when a power supply from a storage battery to the ECU is turned off, a vehicle export destination, a transmission type (manual or automatic), an engine type (natural aspirated or turbo charged), a vehicle identification code (VIN), malfunction information and the like.
U.S. Pat. No. 4,896,263 teaches to use a single EEPROM for multiple CPUs so that the EEPROM is shared by the multiple CPUs. In this instance, as shown in FIG. 8, CPUs 11 and 12 are connected to each other through communication lines 14 and 15 and only the CPU 16 is connected to an EEPROM 13 through a signal line 16 in an ECU 10. The CPU 11 retrieves or reads out data from the EEPROM 13 and transmits the retrieved data to the CPU 12 through the communication line 14, when initialization of software is effected. The CPU 11 receives all data of the CPU 12 to be written and stored in the EEPROM 13 through the communication line 15 and transmits the received data to the EEPROM 13.
In this ECU 10, as the EEPROM 13 is accessed via the CPU 11, the EEPROM access time of the CPU 11 increases and the communication data between the CPUs 11 and 12 increases. Further, in the initialization operation of the software, the CPU 12 is enabled to use the data of the EEPROM 13 only after the retrieved data are transmitted from the CPU 11, thus resulting in a time delay of using the retrieved data in the CPU 12.